Do you mean PR5 and PR6? If so, then it's what is known as page rank, how google supposedly values the importance of a website, with PR0 being the lowest and PR10 being the highest.
To increase your PR you are going to need to get backlinks from relevant sites (sites similar to yours).
Make sure you are putting your links in websites that have to do with your niche. For example in directories under the category of your website
If your page get a link from a PR7,8 page or get a lot of links from a lot of pr3,4,5 pages then your page will be valued 5,6.
focus on quality above all else. a few quality links will do your website much more good than a hundred crappy links
The PageRank is a value that Google gives to a page, based on the number and type of backlinks into the page. So obviously in order to increase the PR of a page you need to get websites with a high PR to link back to that page.